Research On Conducted EMI Analysis And Inhibition Technology Of Switching Power Supply

With the improvement of switch frequency and power density of switch power supply,conduction of switch power supply EMI problem is particularly prominent and important.Transformer distributed capacitance and grounding impedance as a coupling channel link of switch power supply will affect the conducted EMI. Based on the two problems are studied.Firstly, conducted EMI flow path of the switching power supply is analyzed, and switching power supply common mode conducted EMI model is established. The influence of the transformer distributed capacitance and the grounding impedance of common mode conducted EMI current is analyzed. It can be seen that with the increase of distributed capacitance, the common-mode current increased. And, with the increase of the grounding impedance the common-mode interference current is reduced. So, we need to study how to reduce the distributed capacitance and the grounding impedance influence on conducted EMI.In this paper, the transformer distributed capacitance network structure model is established considering all number of turns of the distributed capacitance between the transformer. And put forward a kind of transformer distributed capacitance network model parameter extraction method based on MAXWELL software, the distributed capacitance of transformer can be calculated by combining the method and modeling method. And then through the. two-port network experiment extracted the distributed capacitance of transformer,compared the results, verify the correctness of the presented modeling method. And the sectional winding method is used to reduce the distributed capacitance between primary and secondary of the transformer, thus reduce conduction switch power supply EMI. Sectional winding method is verified can reduce the conduction of switch power supply EMI by simulation and experiment.At the same time, based on high-power supply cabinet put oneself in another's position as a grounding system, simulated the impedance on the panel of power supply cabinet, verified the influence of frequency on the ground impedance,the influence of panel hole shape and size on the ground impedance, and the influence of the panel hole location layout on the ground impedance. By comparing different ground impedance, analyzed the influence of hole layout on ground impedance.